Computer networks facilitate the communication of electronic messages from sender computers to recipient computers. Electronic messages include communications, such as email, text messages, digital voice messages, and instant messages. Electronic messages can include electronic files and/or links to electronic files. A link is a text-based reference to a location of a computer resource on a network and may include a uniform resource locator (URL), a domain address such as a Simple Mail Transfer Protocol (SMTP) address or a Hypertext Transfer Protocol (HTTP) address, or an Internet Protocol (IP) address, for example. Electronic files may include text, graphics, digital images, digital audio, sensor data, or any combination of different types of digital content.
Messaging systems implemented on a network control the flow of electronic messages from sender computers to recipient computers. Messaging systems can include server computers, such as mail servers, configured with software applications such as message routers, load balancers, and message transfer agents (MTAs). Messaging systems are often configured with security software that is designed to protect recipient computers and the network from security risks and other issues that may be associated with particular electronic messages.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section.